Thyrotropin release hormone (TRH). The difficulties in getting a clear picture of the mode of synthesis persist. The main obstacles are: 1) separation of isotope-marked byproducts from synthetic products; 2) content of potent specific degrading peptidases in hypothalamic tissue. Refining of analytic procedures and use of inhibitors of peptidases are being tried out. Tyrocidine enzymes. Isolation of the pantetheine-peptidyl transfer protein will be continued. Present molecular weight data are indicative of an aggregation of subunits of ca. 15,000-18,000. Studies on the racemization of phenylalanine are in progress. The mechanism of pyrophosphorylation by ATP of GTP/GDP in stringent E. coli by the ribosomal wash factor plus or minus ribosome will be studied. A start will be made on the mechanism of valinomycin and rhodotorulic acid, where a biosynthesis by way of thiol-linked intermediaries has been considered.